Paul G. Pringle

1,8-bis(diphenylphosphino)naphthalene : a rigid chelating, diphosphine analogue of proton sponge

Abstract The synthesis of the new diphosphine, 1,8-bis(diphenylphosphino) naphthalene ( 1a ), and its X-ray crystal structure are reported. Protonation of 1a gives a fluxional species to which a PP bonded structure is assigned. Despite the strain apparent in the solid state due to the proximity of the diphenylphosphino groups, it appears that 1a has a normal coordination chemistry with platinum(II) and palladium(II).

Probing the bonding of phosphines and phosphites to platinum by NMR. Correlations of 1J(PtP) and Hammett substituent constants for phosphites and phosphines coordinated to platinum(II) and platinum(0)

Abstract The values of 1 J (PtP) have been measured for the platinum(II) complexes cis -[PtCl 2 L 2 ] and cis -[PtMeClL 2 ] and the platinum(0) complexes [PtL(norbornene) 2 ] and [PtL 2 (norbornene)] where L = P(C 6 H 4 Z-4) 3 and [PtL 2 (norbornene)], [PtL 3 ] and [PtL 4 ] where L = P(OC 6 H 4 Z-4) 3 and Z = NMe 2 , Ome, Me, H, Cl, CF 3 . When 1 J (PtP) is plotted against the Hammett substituent constant two distinct trends emerge: for platinum(II) the more electron-withdrawing the substituent the smaller the 1 J (PtP), while for platinum(0) the more electron-withdrawing the substituent the larger the 1 J (PtP). These observations are rationalised in terms of the σ and π-bonding components of the platinum-phosphorus bonds.

Synthesis and reactivity of dichloroboryl complexes of platinum(II)

The reaction between [Pt(nbe)3] (nbe=norbornene), two equivalents of the phosphines PPh3, PMePh2 or PMe2Ph and 1 equivalent of BCl3 affords the platinum dichloroboryl species [PtCl(BCl2)(PPh3)2], [PtCl(BCl2)(PMePh2)2] and [PtCl(BCl2)(PMe2Ph)2]. All three complexes were characterised by X-ray crystallography and reveal that the boryl group lies trans to the chloride. With PMe3 as the phosphine, the complex [PtCl(BCl2)(PMe3)2] is isolated in high yield as a white crystalline powder although crystals suitable for X-ray crystallography were not obtained. Crystals were obtained of a product shown by X-ray crystallography to be the unusual dinuclear species [Pt2(BCl2)2(PMe3)4(micro-Cl)][BCl4] which reveals an arrangement in which two square planar platinum(II) centres are linked by a single bridging chloride which is trans to a BCl2 group on each platinum centre. The reaction of [PtCl(BCl2)(PMe3)2] with NEt3 or pyridine (py) affords the adducts [PtCl{BCl2(NEt3)}(PMe3)2] and [PtCl{BCl2(py)}(PMe3)2], respectively, both characterised spectroscopically. The reaction between [PtCl(BCl2)(PMe3)2] and either 4 equivalents of NHEt2 or piperidine (pipH) results in the mono-substituted boryl species [PtCl{BCl(NEt2)}(PMe3)2] and [PtCl{BCl(pip)}(PMe3)2], respectively, the former characterised by X-ray crystallography. Treatment of either [PtCl(BCl2)(PMe3)2] (in the presence of excess NEt3) or [PtCl{BCl(NEt2)}(PMe3)2] with catechol affords the B(cat) (cat=catecholate) derivative [PtCl{B(cat)}(PMe3)2] which is also formed in the reaction between [Pt(PMe3)4] and ClB(cat) and also from the slow decomposition of [Pt{B(cat)}2(PMe3)2] in dichloromethane over a period of months. The compound [Pt{B(cat)}2(PMe3)2] was prepared from the reaction between [Pt(PMe3)4] and B2(cat)2.

Computational Kinetics of Cobalt‐Catalyzed Alkene Hydroformylation

Density functional theory, coupled-cluster theory, and transition state theory are used to build a computational model of the kinetics of phosphine-free cobalt-catalyzed hydroformylation and hydrogenation of alkenes. The model provides very good agreement with experiment, and enables the factors that determine the selectivity and rate of catalysis to be determined. The turnover rate is mainly determined by the alkene coordination step.

Phosphonite ligands for enantioselective copper(I)-catalysed conjugate addition of diethylzinc to enones

A wide variety of novel chiral monodentate phosphonite ligands derived from binaphthol and biphenanthrol have been tested as ligands in the copper(I)-catalysed conjugate addition of diethylzinc to enones, resulting in e.e.s of up to 82% for chalcone.

Chiral aryl diphosphites: a new class of ligands for hydrocyanation catalysis

The new diphosphite 1 derived from R-2,2′-binaphthol and its nickel(0) complex are described; optical yields for the hydrocyanation of norbornene are 38%.

Water soluble, zero-valent, platinum–, palladium–, and nickel–P(CH2OH)3 complexes:catalysts for the addition of PH3 to CH2O

The phosphine P(CH2OH)3 forms water soluble complexes of the type[M{P(CH2OH)3}4](M pt, Pd, or Ni) which are catalysts for the addition of PH3 to CH2O and the Pt complex is readily protonated by water;the crystal structure of the Pd complex is also described.

Synthesis and reactions of the heterobimetallic complex [ClPd(µ-Ph2PCH2PPh2)2PtCl]

New methods of preparing [ClPd(µ-dppm)2PdCl](1b)(dppm = Ph2PCH2PPh2) are described, such as reduction of [PdCl2(dppm-PP′)] with zinc dust, formic acid, or hydrazine. Treatment of [Pd2Cl2(η3-allyl)2] with an excess of dppm gives pure (1b) readily, albeit in only 45% yield. [(η3-C3H5)ClPd(µ-dppm)PdCl(η3-C3H5)] is also described. The best route to (1b) is to treat [Pd(PPh3)4] and dppm with [PdCl2(NCPh)2], giving yields of 80–90%. Similar treatment of [Pt(PPh3)4] and dppm with [PtCl2(NCBut)2] gives [ClPt(µ-dppm)2PtCl](la), often contaminated, however, with ca. 10% of [PtCl2(dppm-PP′)]. Treatment of dppm and [Pd(PPh3)4] with [PtCl2(NCBut)2] gives the previously unknown heterobimetallic complex [ClPt(µ-dppm)2PdCl](1c) in excellent yield (83–92%) and purity. The corresponding dibromide, di-iodide, and dithiocyanate were prepared from (1c) by metathesis. Complex (1c) readily reacts with some small molecules, SO2, CO, MeO2CCCCO2Me or CS2, to give ‘A-frames’[ClPt(µ-SO2)(µ-dppm)2PdCl], [ClPt(µ-CO)(µ-dppm)2PdCl], [ClPt(µ-MeO2CCCCO2Me)(µ-dppm)2PdCl], and [ClPt(µ-CS2)(µ-dppm)2PdCl] respectively. The addition of SO2, CO, or CS2 is reversible and SO2 promotes or catalyses the displacement of CO. Hydrogen-1, 31P-{1H}, and 195Pt n.m.r. data are given and discussed as are some i.r. data.

Diphosphine analogues of proton sponge: X-ray crystal structure of [Pd(η3-allyl)(dppn)]BF4·CH2Cl2 (dppn = 1,8-bis(diphenylphosphino)naphthalene)

Abstract The X-ray crystal structure of [Pd(η3-ally)dppn)]BF4·CH2Cl2 (1) where dppn = 1,8-bis(diphenylphosphino)naphthalene is reported. Comparison of the conformation of the ligand in 1 with that in the free state shows that there is a relief of strain on complexation analogous to the relief of strain observed upon protonation of proton sponge.

Synthesis and properties of new tris(cyanoethyl)phosphine complexes of platinum (0,II), palladium (0,II), iridium (I) and rhodium (I).: Conformational analysis of tris(cyanoethyl)phosphine ligands

Abstract The tris(cyanoethyl)phosphine (tcep) complexes trans -[PtCl 2 (tcep) 2 ], cis -[PtMe 2 (tcep) 2 ], and trans -[PtMeCl(tcep) 2 ] are prepared by treatment of the corresponding [PtXY(cod)] (cod=1,5-cyclooctadiene) with tcep. Reduction of trans -[PtCl 2 (tcep) 2 ] with NaBH 4 gives trans -[PtHCl(tcep) 2 ] which, in the presence of tcep and NEt 3 , gives the coordinatively unsaturated platinum(0) complex [Pt(tcep) 3 ]. This coordinatively unsaturated species is also formed when [Pt(norbornene) 3 ] reacts with tcep. [Pt(tcep) 3 ] is very unreactive compared to its PEt 3 analogue: it is air-stable and does not react with further tcep to form an 18-electron species. It is protonated by HBF 4 ·OEt 2 to form [PtH(tcep) 3 ]BF 4 . The complex trans -[PdCl 2 (tcep) 2 ] is made from [PdCl 2 (NCPh) 2 ] and tcep and the derivatives trans -[PdX 2 (tcep) 2 ] (X=Br or I) are made by metathesis of the dichloro complex. Reduction of trans -[PdCl 2 (tcep) 2 ] with LiOMe in the presence of tcep gave the palladium(0) complex [Pd(tcep) 3 ] which, like its platinum(0) analogue, undergoes exchange with free tcep on the NMR timescale. The palladium complex reacts with dibenzylideneacetone (dba) to form [Pd( η 2 -dba)(tcep) 2 ]; the same product is formed in the reaction of [Pd( η 2 -dba) 2 ] and tcep. Reaction of [Pd 2 Cl 2 ( η 3 -C 3 H 3 ) 2 ] and tcep gives [PdCl(tcep)( η 3 -C 3 H 3 )] or [Pd(tcep) 2 ( η 3 -C 3 H 3 )]Cl depending on stoichiometry. The rhodium(I) and iridium(I) complexes trans -[MCl(CO)(tcep) 2 ], [MCl(tcep)(cod)] and [MCl(tcep) 3 ] are all readily made from tcep and an appropriate precursor. All new compounds have been fully characterised by a combination of elemental analysis, IR, 31 P, 13 C, 1 H and 195 Pt NMR spectroscopy. The crystal structure of [IrCl(tcep) 3 ] as a MeCN solvate shows a distorted square planar coordination geometry ( trans angles at Ir(I) ca. 164°, cis P–Ir–P av. 96°, cis P–Ir–Cl av. 85°). Analysis of the conformations of tcep ligands in this and other published tcep complexes shows there is a preference for conformations in which aaa, aag or g + g − (a=anti, g=gauche) arrangements of the three M–P–C–C chains are avoided.